my bro's bike had 7 speed and 36 spokes... is it possible his hub can fit to my 8 speed and 32 spokes?
sprocket spacing between 7 and 8 speed is almost identical therefore 8sp is one sprocket wider than 7sp. For this reason, you can't use a 7speed hub for 8speed sprockets unless you miss one off. you would then also need to ensure the gears are set up safely, so the chain can't be shifted into the spokes.
You’ll need: Same hub width, same wheel diameter, rim width which fits your brakes (if you have rim brakes), tire width narrow enough to fit your brakes and frame. The number of spokes doesn’t matter for compatibility.
You’ll probably have to adjust the rear derailleur and you’ll only be able to use 7 of the 8 sprockets. It’s possible because 7 and 8 speed have the same sprocket spacing. I’ve used an 8 speed shifter for a 7 speed cassette, so I see no reason why it shouldn’t be possible the other way around.